The present invention relates generally to a multi-piece expansion ring used to expand the size of a portable oven, and to a unique clip used to hold the pieces of the expansion ring together. More specifically, the present invention relates to such an expansion ring/clip combination which securely holds the expansion ring segments together, but allows for easy disassembly of the expansion ring for cleaning and storage.
The concept of using expansion rings to increase the cooking capacity of a portable oven is disclosed in U.S. application Ser. No. 325,157 filed Mar. 17, 1989 and assigned to the same assignee as the present invention. The present invention it is particularly useful with the oven disclosed in Ser. No. 325,157. To the extent that the disclosure of that application is necessary to an understanding of the present invention, it is incorporated by reference herein.
It is desirable for a number of reasons to form an expansion ring out of two or more segments. Such a multi-segment design is easier to manufacture. It is also more compact for shipping and storage purposes, and is easier for the user to clean.
When such a multi-piece extension ring is used, some means must be provided to connect the segments together. One such means which is known is the clip shown in FIG. 1. This clip, which is made of aluminum, has a generally planar front face 2 and a rounded back face 4. A slot 6 is formed along the front face of the clip. The expansion ring segments (not shown) have projections extending along the free ends thereof. The projections are shaped so that when two expansion ring segments are placed together, the projections of the two segments together form a shape generally the same as that of slot 6. Thus, the clip can be slid over the two projections so as to hold the segments together.
The clip of FIG. 1 suffers from numerous disadvantages. Several disadvantages result from the use of aluminum for the clip. One, aluminum has high thermal conductivity. Thus, when the oven is heated up, the clips tend to heat up quickly and retain that heat. These hot clips are potentially dangerous to the user, who can be burned.
Two, the expansion ring segments are made of plastic, which has a different thermal expansion rate than the aluminum of the clips. Thus, when the oven is used, the plastic expansion ring segments expand faster than the clips. This causes great stress to be placed on the projections, which can crack under the pressure.
Another related problem is that the only thing holding the clip in place is friction. If the clip is designed to fit tightly on the projections so as to remain securely in place, then the cracking problem referred to in the previous paragraph is particularly troublesome. One the other hand, if the clip is designed to only loosely fit over the projections, the clip is not held securely, and has a tendency to fall off.
One solution which has been suggested is shown in FIG. 2. The only difference between the clip of FIG. 2 and that of FIG. 1 is the use of two small bumps 8 located within space 6. The bumps are designed to cooperate with two small detents located on the projections of the expansion ring segments.
However, this clip, which is also made of aluminum, still suffers from disadvantages. Importantly, when the clip is slid on and off numerous times, the metal bumps on the clip eventually form a groove in the softer plastic of the expansion ring segments. This loosens the fit of the clip on the projections, so that eventually the bumps and detents would cease to served any function.
Finally, the aluminum clips shown in FIGS. 1 and 2 are very labor intensive, and thus expensive, to produce.